Inr. /. .\urs. Srud.. Vol Pnnred tn Great Bruin.
27. No. 3. pp. 157-265.
1990 5
0020.3189/W 53.00 + 0.00 I990 Pergamon Press plc
Sequential and simultaneous breast pumping: a comparison * KATHLEEN
G. AUERBACH,
Ph.D.,
IBCLC
Department of Pediatrics, University of Chicago, 5841 S. Maryland Ave.. Chicago, IL 60637, C.K.4.
Abstract-This study compared sequential single-breast pumping with simultaneous double-breast pumping using an interrupted time series design to determine if (a) milk volume differed by pumping regimen; (b) the time needed to pump the breasts differed by pumping regimen; and (c) the milk fat concentrations differed by pumping regimen. In both limited and unlimited pumping sessions, the simultaneous double pumping option obtained higher mean milk volumes, reaching statistical significance in three of the four comparisons. Differences in milk fat concentrations were not statistically significant, when simultaneous breast pumping occurred, as compared with sequential pumping. Mothers’ preferences regarding pumping regimen influenced mean milk volumes obtained in the direction of the women’s preferences.
Introduction
Mothers who wish to continue breastfeeding when they have returned to work or school often have difficulty maintaining an adequate milk supply unless they have learned to obtain milk during the period when they are separated from the baby (Auerbach, 1984; Auerbach and GUSS, 1984; Frederick and Auerbach, 1985). In addition, women with premature infants often need an efficient way of obtaining milk while preparing for the time when the baby can nurse. Options that mothers have used with varying degrees of success include hand expression, hand-operated breast pumps, or electrically-operated breast pumps. Of the pumps Johnson (1983) evaluated, the electrically-operated model was found to be the most comfortable and most efficient. Green and colleagues (1982) also found that *Funded in part by Medela, Inc., 6711 Sands Road, PO Box 386, Crystal Lake, IL 60014. U.S.A. 257
258
KATHLEEN
G. A UERBACH
an electric breast pump obtained more milk within a IO-min expression period when compared with hand-operated pumps that were used for the same length of time. While many women choose to breastfeed, even under circumstances that may include frequent and/or prolonged periods of separation requiring use of hand expression or a breast pump, the time needed to mechanically obtain milk from the breasts may be such that women will choose not to do so. Other factors include finding a place to pump that is accessible and private. One employer found that providing space for, and assistance in, the use of an electric breast pump resulted in an increase in breastfeeding duration among women employees, and a slightly earlier return to employment by those workers (Katcher and Lanese, 1985). Another question raised, but rarely answered pertains to the fat concentrations found in pumped milk; specifically, do such fat concentrations (Lucas et al., 1978; Lemons el al., 1980) remain the same when different pumping regimens are used? Recently, manufacturers of electrically-operated breast pumps have offered a simultaneous double-pump option to single-breast, sequential, pumping. This option is designed to shorten the time needed to obtain milk. Theoretically, such a pattern of pumping works in the same manner as simultaneous nursing of twin infants, whose mothers often report sensations of multiple milk ejection responses in a single feeding, and whose milk volume has been reported to exceed that of mothers of single infants (Saint et al., 1986). When mothers pump a single breast, they may lose the drip milk that leaks from the unpumped side while they concentrate on collecting milk from the breast being pumped. Pumping one side at a time may not provide the same degree of stimulation that simultaneous pumping provides. Furthermore, anecdotal comments from mothers familiar with pumping suggests that the amount of time needed to collect the same amount of milk may be less than when simultaneous pumping and collection is used. Finally, one group of investigators has reported that the concentration of the fatty portion of milk obtained with simultaneous pumping is higher than that obtained when each breast is pumped in sequence (Neifert and Seacat, 1985). Such a finding may be important in situations when mothers are pumping for compromised infants where optimizing growth is critical.
Study Questions I sought to answer three questions with this study: (1) is the volume of pumped milk lower with sequential single-pumping than with simultaneous double-pumping; (2) does sequential single-pumping take more time to obtain a similar amount of milk compared with a simultaneous double-pumping experience and (3) is the concentration of the fatty portion of milk lower with a sequential single-pumping regimen than with simultaneous double-pumping?
Methods
In order to answer the questions mentioned above, each mother recruited to participate in the study was asked to pump milk from her breasts on four separate occasions with an electric intermittent vacuum pump, using one of four possible regimens on each occasion: (a) 5-min sequential pumping (the breast pumped first was randomly assigned as determined by a table of random numbers); 5-min simultaneous pumping; unlimited sequential pumping (the breast pumped first was randomly assigned); or unlimited simultaneous pumping. The style of pumping used for each pumping session was randomly assigned, with each mother
SEQUENTIAL
AND
SIMULTANEOUS
BREAST
PUMPING
259
serving as her own control. Sequential pumping was defined as pumping each breast alone in sequence, left and then right or right and then left. Simultaneous pumping was defined as pumping both breasts at the same time. Unlimited pumping was defined as the total time period when the mother observed milk entering the pump collection chamber from at least one breast. In addition to recording milk volumes obtained from each breast at each pumping session, and to obtaining creamatocrit readings from milk samples obtained from each breast at each pumping session, a structured interview obtained information about current breastfeeding patterns, including its frequency of occurrence, and concluded with an inquiry as to the mother’s preferred method of expressing her breast milk. The study protocol was reviewed and approved by the Clinical Investigations Committee of the University of Chicago Medical Center. The intermittent electric breast pump (# 015) and the pumping kits ( # 800005OS) were provided by Medela, Inc. The mothers used the kit assigned to them throughout the study period, which they kept as a non-monetary payment for their participation in the study. Each pumping kit contained the parts necessary both to pump sequentially one breast at a time and to pump simultaneously. The total volume of milk obtained was measured according to the calibration marks on the milk collection bottles that are part of the pumping kit. Following each pumping session, the milk obtained from each breast was mixed and a 75mm capillary tube of milk was drawn off, spun in an International Micro-Capillary Centrifuge, Model MB for 15 minutes and measured using a Lancer Micro-Hematocrit Capillary Tube Reader. The time of day of each pumping session, and the duration of each pumping session was recorded. The remainder of the milk obtained at each pumping session was given to the mother to take home for later use. Sample population
Twenty-six women were recruited to participate from among patients who had delivered at the Chicago Lying-in Hospital and the surrounding community. All of the women were anticipating returning to work or school and planning to pump their breasts during their periods of separation, or were already experiencing such regular separations. All 26 women completed the study; however, the data reported omit one mother of twins who participated, although no statistically significant differences were found between the outcome of her pumping sessions and the other participants. Twenty women (80%) were primiparas; five (20%) were multiparas; each of the multiparous women had given birth to two healthy babies. All 25 infants, for whom the mothers were pumping their milk, were healthy and thriving; all had been born full term. The participants ranged in age from 21 to 42 years (modal and median age was 3 1; standard deviation was 5.5 years). Two women (SVo)were Asian; 6 were Black (24Vo); the remaining participants (68%) were White. Twenty-three participants (92%) were married; two women were single. At the time of the study, the infants ranged from 5 to 35 weeks in age (median age was 8 weeks; mean age was 12 weeks); 15 infants (60%) were exclusively human milk-fed; 6 (24%) were receiving human milk and artificial formula; 3 (12%) were receiving human milk and solid foods; and one infant was receiving human milk with artificial formula and solid foods. On weekdays, most infants were breastfed seven times (mean number of feedings: 6; mode was 8); on weekends, the average number of breastfeedings increased to eight (mean and modal number of feedings was 8). As expected, the younger the infant, the greater the number of breastfeedings.
KATHLEEN
260
G. AUERBACH
The likelihood of use of feedings other than human milk increased with the infant’s age (Table 1). When artificial formula or solid foods were offered, their amounts coincided with periods of separation from the mother due to her employment or student status. Only one mother reported offering more than two 4-ounce bottles/day of non-human milk; her baby also received 1 tablespoon of cereal once a day in her absence. In all other cases, only one or two 4-ounce bottles of artificial formula or some kind of solid food was offered when the mother was not available to breastfeed. Table I. Infant age and type of feedings offered Type of feedings* HM only HM+AF HM + solids and/or AF Total
< 1I weeks
Age of infants I I-20 weeks > 20 weeks
11 (73%) 3 (20%) 1 (17%) IS (60070)
3 2 I 6
(50%) (33%) (17%) (24%)
I I 2 4
(25%) (25%) (50%) (16%)
Total I5 6 4 25
(60%) (24010) (1670) (100%)
*HM = Human milk, AF = artificial formula.
Results
Maternal and infant factors Sociodemographic variables such as maternal age, parity and ethnic group were unrelated to the volume of milk obtained during the study sessions. Experience with pumping prior to study participation also was unrelated to milk volumes obtained. The age of the baby at the time of the mother’s entry into the study influenced mean milk volumes obtained. For three of the four pumping regimens, mothers whose babies were 12-15weeks old obtained the most milk at each pumping session. Within specific age groupings, mothers with infants under 8 weeks obtained the most milk only when using the unlimited simultaneous pumping pattern (Table 2). Table 2. Age of baby and mean milk volumes obtained by pumping regimen Pumping regimen 5-Minute 5-Minute Unlimited Unlimited
sequential simultaneous sequential simultaneous
~8 weeks 8-11 weeks 12-15 weeks 16+ weeks
~8 weeks (8) 81’ 109 99 137 one-way X2 15.4 10.08 2.34 8.74
Mean milk volumes S-II weeks 12-15 weeks (g) (9) 83 120 119 90 df 3 3 3 3
I21 I25 141 119
16+ weeks (g) 84 101 122 119
0.04 0.02 ll.S.
0.05
Sequential versus simultaneous pumping To answer the first two questions, milk volume during each pumping regimen was measured, with each woman serving as her own control. As noted in Fig. 1.5min sequential breast pumping yielded the smallest amount of milk from this sample of lactating mothers,
SEQUENTIAL
AND
SIMULTANEOUS
BREAST
PUiCtPING
261
followed by timed simultaneous breast pumping. When sequential pumping was allowed to proceed until no more milk was entering the pump collection chamber, slightly more milk was obtained; the greatest amount of milk was collected when simultaneous pumping was allowed to continue until milk was no longer entering the collection chamber. Statistically significant differences between the four pumping regimens occurred when comparing 5-min sequential with 5-min simultaneous pumping, untimed sequential pumping, and untimed simultaneous pumping. The first question of the study thus was answered in favor of simultaneous pumping during both time-limited and unlimited pumping regimens. Timed verses untimed pumping Two pumping regimens lasted until the mother no longer observed milk dripping from at least one breast.* During the sequential pumping period, mean pumping time was 10.6 min (range was 7-22 min; mode was 7; median was 9). During the simultaneous pumping period, mean duration of pumping was 12 min (range was 5-22 min; mode was 9; median was 12). Of the 25 participants, only three (12%) pumped the same length of time for both sequential and simultaneous regimens. Seventeen women (68%) observed milk entering the pump collection chamber for a longer period with simultaneous than with sequential pumping. Five women (20%) collected milk for a longer period with sequential than with simultaneous pumping. Pumping sessions longer than 5 min were found to be more productive than shorter sessions. However, pumping duration was not related directly to milk volume. The highest mean milk volumes during sequential pumping sessions were obtained when mothers pumped for 10 to 15 min. When simultaneous pumping was used, maximum milk volumes were obtained when pumping times lasted from 7 to 12 min. Pumping periods longer than 15 min, regardless of the regimen used, did not result in the largest milk volumes. When the women pumped sequentially, the untimed session yielded significantly more milk than when the women pumped in this same manner for only five minutes on each breast. When the women pumped both breasts simultaneously, the difference in milk volumes obtained between limited and unlimited sessions was not statistically significant. In addition, although simultaneous pumping resulted in a higher mean milk volume than sequential pumping when the pumping period was allowed to last as long as the mother’s milk was entering the pump collection chamber, this difference was not statistical!y significant (Fig. 1). Thus, the second question was answered in favor of untimed pumping for both regimens, although the difference was greatest between sequential pumping comparison groups. Fat concentrations and pumping regimens Milk fat concentration was determined by measuring creamatocrits from each sample of milk from each breast at each pumping session. Creamatocrit readings varied minimally between breasts and across pumping sessions for each woman. However, the range between women was wide: O-17070. Mean readings were in the 6-7% range across all pumping regimens. No statistically significant differences were identified between breast samples or by pumping regimens, although 28% of all creamatocrit readings during the 5-min sequential *Unlimited pumping sessions ranged from 7 to 22 min.
KATHLEEN
262
t-lean: LE.:
G. AUERBACH
S-minute
5-mmute
Unllmlted
UnllmGd
Squential
Simultaneous
Sequential
Simultaneous
88.56
I t 1.28
I 14.36
126.04
9.94
13.18
13.28
I 4.84
Paired two-tailed t-test differences between the means. S-minute sequential vs. S-minute simultaneous:
2.37
S-minutesequential
vs. unllmitedsquent~al:
2 39
9’.02
5-minutesaquential
vs. unlimiteds~multaneous
2 99
pc.006
S-minutesimultaneous
vs. unlimited simultaneous.
9c.02
I.40
n.5
S-minute simultaneous vs. unlfmited sequential.
0 28
ns.
Unlimitedsequential
1.07
n.s.
vs. unlimited simultaneous
pumpings were less than 5’70, compared with 18% or fewer readings at this same level in the other pumping sessions. In addition, 16% of the samples obtained during unlimited simultaneous pumping had creamatocrit readings of 13% or higher, compared with 10% of readings at this level when other pumping regimens were used (Table 3). Table
3. Creamatocrit
readings by pumping regimen used
Pumping regimen
Range WI
SMinute 5-Minute Unlimited Unlimited
o-13 o-17 o-14 o-15
sequential simultaneous sequential simultaneous
Creamatocrit Median 6 6-7 6-7 7-8
readings Mean 6.52 7.26 7.18 7.70
Mothers’ preference of pumping regimen In addition to the quantitative measures reported above, the mothers were asked which pumping regimen they preferred and why. By a margin of three to one in this study, women preferred the double pump system over the single sequential option. In nearly all cases where the double-pump system was preferred, the amount of milk obtained and/or the woman’s perception that such pumping took less time, were mentioned. This preference held even when controlling for the participants’ milk volumes during the single and double pumping sessions. For example, during the timed pumping sequences, 67% of the women who’obtained more milk when pumping sequentially still preferred the simultaneous double
SEQUENTIAL
AND SIMULTANEOUS
BREAST
PUMPING
263
pump option. Of those women who obtained more milk when using the double pump option, 87% preferred that pattern over single sequential pumping. The same pattern was observed when the pumping sessions were allowed to proceed until each participant had ceased obtaining milk. Mothers who preferred the single-breast pumping option mentioned that they felt ‘cow-like’, that pumping both breasts simultaneously was awkward for them, or that they preferred to have one hand free for other activities even when they were aware that they obtained more milk using the simultaneous system. Among mothers who preferred to pump sequentially, mean milk volumes declined slightly when they used simultaneous pumping, whether they were timed or untimed (Table 4). By contrast, women who preferred simultaneous pumping experienced a marked increase (26%) in milk volumes obtained during timed pumpings, and a somewhat smaller increase (17%) in milk volumes during unlimited pumping regimens when they pumped both breasts simultaneously. Table 4. Pumping preferences by regimen and milk volumes obtained Pumping regimen
5-Minute J-Minute Unlimited Unlimited
sequential simultaneous sequential simultaneous
Milk volumes obtained Simultaneous Sequential Range Mean Mean Range (g) (9) (g) (9) 26-140 25-130 48-152 21-132
78 65 (-17%)’ 89 69 (-13%)
25-240 32-230 27-287 50-297
R
R?
F
Timed pumping sessions x pumping preference:
0.43
0.18
2.55
p-value < 0.05 >O.lO
Untimed pumping sessions x pumping preference:
0.50
0.25
3.69
27. No. 3. pp. 157-265.
1990 5
0020.3189/W 53.00 + 0.00 I990 Pergamon Press plc
Sequential and simultaneous breast pumping: a comparison * KATHLEEN
G. AUERBACH,
Ph.D.,
IBCLC
Department of Pediatrics, University of Chicago, 5841 S. Maryland Ave.. Chicago, IL 60637, C.K.4.
Abstract-This study compared sequential single-breast pumping with simultaneous double-breast pumping using an interrupted time series design to determine if (a) milk volume differed by pumping regimen; (b) the time needed to pump the breasts differed by pumping regimen; and (c) the milk fat concentrations differed by pumping regimen. In both limited and unlimited pumping sessions, the simultaneous double pumping option obtained higher mean milk volumes, reaching statistical significance in three of the four comparisons. Differences in milk fat concentrations were not statistically significant, when simultaneous breast pumping occurred, as compared with sequential pumping. Mothers’ preferences regarding pumping regimen influenced mean milk volumes obtained in the direction of the women’s preferences.
Introduction
Mothers who wish to continue breastfeeding when they have returned to work or school often have difficulty maintaining an adequate milk supply unless they have learned to obtain milk during the period when they are separated from the baby (Auerbach, 1984; Auerbach and GUSS, 1984; Frederick and Auerbach, 1985). In addition, women with premature infants often need an efficient way of obtaining milk while preparing for the time when the baby can nurse. Options that mothers have used with varying degrees of success include hand expression, hand-operated breast pumps, or electrically-operated breast pumps. Of the pumps Johnson (1983) evaluated, the electrically-operated model was found to be the most comfortable and most efficient. Green and colleagues (1982) also found that *Funded in part by Medela, Inc., 6711 Sands Road, PO Box 386, Crystal Lake, IL 60014. U.S.A. 257
258
KATHLEEN
G. A UERBACH
an electric breast pump obtained more milk within a IO-min expression period when compared with hand-operated pumps that were used for the same length of time. While many women choose to breastfeed, even under circumstances that may include frequent and/or prolonged periods of separation requiring use of hand expression or a breast pump, the time needed to mechanically obtain milk from the breasts may be such that women will choose not to do so. Other factors include finding a place to pump that is accessible and private. One employer found that providing space for, and assistance in, the use of an electric breast pump resulted in an increase in breastfeeding duration among women employees, and a slightly earlier return to employment by those workers (Katcher and Lanese, 1985). Another question raised, but rarely answered pertains to the fat concentrations found in pumped milk; specifically, do such fat concentrations (Lucas et al., 1978; Lemons el al., 1980) remain the same when different pumping regimens are used? Recently, manufacturers of electrically-operated breast pumps have offered a simultaneous double-pump option to single-breast, sequential, pumping. This option is designed to shorten the time needed to obtain milk. Theoretically, such a pattern of pumping works in the same manner as simultaneous nursing of twin infants, whose mothers often report sensations of multiple milk ejection responses in a single feeding, and whose milk volume has been reported to exceed that of mothers of single infants (Saint et al., 1986). When mothers pump a single breast, they may lose the drip milk that leaks from the unpumped side while they concentrate on collecting milk from the breast being pumped. Pumping one side at a time may not provide the same degree of stimulation that simultaneous pumping provides. Furthermore, anecdotal comments from mothers familiar with pumping suggests that the amount of time needed to collect the same amount of milk may be less than when simultaneous pumping and collection is used. Finally, one group of investigators has reported that the concentration of the fatty portion of milk obtained with simultaneous pumping is higher than that obtained when each breast is pumped in sequence (Neifert and Seacat, 1985). Such a finding may be important in situations when mothers are pumping for compromised infants where optimizing growth is critical.
Study Questions I sought to answer three questions with this study: (1) is the volume of pumped milk lower with sequential single-pumping than with simultaneous double-pumping; (2) does sequential single-pumping take more time to obtain a similar amount of milk compared with a simultaneous double-pumping experience and (3) is the concentration of the fatty portion of milk lower with a sequential single-pumping regimen than with simultaneous double-pumping?
Methods
In order to answer the questions mentioned above, each mother recruited to participate in the study was asked to pump milk from her breasts on four separate occasions with an electric intermittent vacuum pump, using one of four possible regimens on each occasion: (a) 5-min sequential pumping (the breast pumped first was randomly assigned as determined by a table of random numbers); 5-min simultaneous pumping; unlimited sequential pumping (the breast pumped first was randomly assigned); or unlimited simultaneous pumping. The style of pumping used for each pumping session was randomly assigned, with each mother
SEQUENTIAL
AND
SIMULTANEOUS
BREAST
PUMPING
259
serving as her own control. Sequential pumping was defined as pumping each breast alone in sequence, left and then right or right and then left. Simultaneous pumping was defined as pumping both breasts at the same time. Unlimited pumping was defined as the total time period when the mother observed milk entering the pump collection chamber from at least one breast. In addition to recording milk volumes obtained from each breast at each pumping session, and to obtaining creamatocrit readings from milk samples obtained from each breast at each pumping session, a structured interview obtained information about current breastfeeding patterns, including its frequency of occurrence, and concluded with an inquiry as to the mother’s preferred method of expressing her breast milk. The study protocol was reviewed and approved by the Clinical Investigations Committee of the University of Chicago Medical Center. The intermittent electric breast pump (# 015) and the pumping kits ( # 800005OS) were provided by Medela, Inc. The mothers used the kit assigned to them throughout the study period, which they kept as a non-monetary payment for their participation in the study. Each pumping kit contained the parts necessary both to pump sequentially one breast at a time and to pump simultaneously. The total volume of milk obtained was measured according to the calibration marks on the milk collection bottles that are part of the pumping kit. Following each pumping session, the milk obtained from each breast was mixed and a 75mm capillary tube of milk was drawn off, spun in an International Micro-Capillary Centrifuge, Model MB for 15 minutes and measured using a Lancer Micro-Hematocrit Capillary Tube Reader. The time of day of each pumping session, and the duration of each pumping session was recorded. The remainder of the milk obtained at each pumping session was given to the mother to take home for later use. Sample population
Twenty-six women were recruited to participate from among patients who had delivered at the Chicago Lying-in Hospital and the surrounding community. All of the women were anticipating returning to work or school and planning to pump their breasts during their periods of separation, or were already experiencing such regular separations. All 26 women completed the study; however, the data reported omit one mother of twins who participated, although no statistically significant differences were found between the outcome of her pumping sessions and the other participants. Twenty women (80%) were primiparas; five (20%) were multiparas; each of the multiparous women had given birth to two healthy babies. All 25 infants, for whom the mothers were pumping their milk, were healthy and thriving; all had been born full term. The participants ranged in age from 21 to 42 years (modal and median age was 3 1; standard deviation was 5.5 years). Two women (SVo)were Asian; 6 were Black (24Vo); the remaining participants (68%) were White. Twenty-three participants (92%) were married; two women were single. At the time of the study, the infants ranged from 5 to 35 weeks in age (median age was 8 weeks; mean age was 12 weeks); 15 infants (60%) were exclusively human milk-fed; 6 (24%) were receiving human milk and artificial formula; 3 (12%) were receiving human milk and solid foods; and one infant was receiving human milk with artificial formula and solid foods. On weekdays, most infants were breastfed seven times (mean number of feedings: 6; mode was 8); on weekends, the average number of breastfeedings increased to eight (mean and modal number of feedings was 8). As expected, the younger the infant, the greater the number of breastfeedings.
KATHLEEN
260
G. AUERBACH
The likelihood of use of feedings other than human milk increased with the infant’s age (Table 1). When artificial formula or solid foods were offered, their amounts coincided with periods of separation from the mother due to her employment or student status. Only one mother reported offering more than two 4-ounce bottles/day of non-human milk; her baby also received 1 tablespoon of cereal once a day in her absence. In all other cases, only one or two 4-ounce bottles of artificial formula or some kind of solid food was offered when the mother was not available to breastfeed. Table I. Infant age and type of feedings offered Type of feedings* HM only HM+AF HM + solids and/or AF Total
< 1I weeks
Age of infants I I-20 weeks > 20 weeks
11 (73%) 3 (20%) 1 (17%) IS (60070)
3 2 I 6
(50%) (33%) (17%) (24%)
I I 2 4
(25%) (25%) (50%) (16%)
Total I5 6 4 25
(60%) (24010) (1670) (100%)
*HM = Human milk, AF = artificial formula.
Results
Maternal and infant factors Sociodemographic variables such as maternal age, parity and ethnic group were unrelated to the volume of milk obtained during the study sessions. Experience with pumping prior to study participation also was unrelated to milk volumes obtained. The age of the baby at the time of the mother’s entry into the study influenced mean milk volumes obtained. For three of the four pumping regimens, mothers whose babies were 12-15weeks old obtained the most milk at each pumping session. Within specific age groupings, mothers with infants under 8 weeks obtained the most milk only when using the unlimited simultaneous pumping pattern (Table 2). Table 2. Age of baby and mean milk volumes obtained by pumping regimen Pumping regimen 5-Minute 5-Minute Unlimited Unlimited
sequential simultaneous sequential simultaneous
~8 weeks 8-11 weeks 12-15 weeks 16+ weeks
~8 weeks (8) 81’ 109 99 137 one-way X2 15.4 10.08 2.34 8.74
Mean milk volumes S-II weeks 12-15 weeks (g) (9) 83 120 119 90 df 3 3 3 3
I21 I25 141 119
16+ weeks (g) 84 101 122 119
0.04 0.02 ll.S.
0.05
Sequential versus simultaneous pumping To answer the first two questions, milk volume during each pumping regimen was measured, with each woman serving as her own control. As noted in Fig. 1.5min sequential breast pumping yielded the smallest amount of milk from this sample of lactating mothers,
SEQUENTIAL
AND
SIMULTANEOUS
BREAST
PUiCtPING
261
followed by timed simultaneous breast pumping. When sequential pumping was allowed to proceed until no more milk was entering the pump collection chamber, slightly more milk was obtained; the greatest amount of milk was collected when simultaneous pumping was allowed to continue until milk was no longer entering the collection chamber. Statistically significant differences between the four pumping regimens occurred when comparing 5-min sequential with 5-min simultaneous pumping, untimed sequential pumping, and untimed simultaneous pumping. The first question of the study thus was answered in favor of simultaneous pumping during both time-limited and unlimited pumping regimens. Timed verses untimed pumping Two pumping regimens lasted until the mother no longer observed milk dripping from at least one breast.* During the sequential pumping period, mean pumping time was 10.6 min (range was 7-22 min; mode was 7; median was 9). During the simultaneous pumping period, mean duration of pumping was 12 min (range was 5-22 min; mode was 9; median was 12). Of the 25 participants, only three (12%) pumped the same length of time for both sequential and simultaneous regimens. Seventeen women (68%) observed milk entering the pump collection chamber for a longer period with simultaneous than with sequential pumping. Five women (20%) collected milk for a longer period with sequential than with simultaneous pumping. Pumping sessions longer than 5 min were found to be more productive than shorter sessions. However, pumping duration was not related directly to milk volume. The highest mean milk volumes during sequential pumping sessions were obtained when mothers pumped for 10 to 15 min. When simultaneous pumping was used, maximum milk volumes were obtained when pumping times lasted from 7 to 12 min. Pumping periods longer than 15 min, regardless of the regimen used, did not result in the largest milk volumes. When the women pumped sequentially, the untimed session yielded significantly more milk than when the women pumped in this same manner for only five minutes on each breast. When the women pumped both breasts simultaneously, the difference in milk volumes obtained between limited and unlimited sessions was not statistically significant. In addition, although simultaneous pumping resulted in a higher mean milk volume than sequential pumping when the pumping period was allowed to last as long as the mother’s milk was entering the pump collection chamber, this difference was not statistical!y significant (Fig. 1). Thus, the second question was answered in favor of untimed pumping for both regimens, although the difference was greatest between sequential pumping comparison groups. Fat concentrations and pumping regimens Milk fat concentration was determined by measuring creamatocrits from each sample of milk from each breast at each pumping session. Creamatocrit readings varied minimally between breasts and across pumping sessions for each woman. However, the range between women was wide: O-17070. Mean readings were in the 6-7% range across all pumping regimens. No statistically significant differences were identified between breast samples or by pumping regimens, although 28% of all creamatocrit readings during the 5-min sequential *Unlimited pumping sessions ranged from 7 to 22 min.
KATHLEEN
262
t-lean: LE.:
G. AUERBACH
S-minute
5-mmute
Unllmlted
UnllmGd
Squential
Simultaneous
Sequential
Simultaneous
88.56
I t 1.28
I 14.36
126.04
9.94
13.18
13.28
I 4.84
Paired two-tailed t-test differences between the means. S-minute sequential vs. S-minute simultaneous:
2.37
S-minutesequential
vs. unllmitedsquent~al:
2 39
9’.02
5-minutesaquential
vs. unlimiteds~multaneous
2 99
pc.006
S-minutesimultaneous
vs. unlimited simultaneous.
9c.02
I.40
n.5
S-minute simultaneous vs. unlfmited sequential.
0 28
ns.
Unlimitedsequential
1.07
n.s.
vs. unlimited simultaneous
pumpings were less than 5’70, compared with 18% or fewer readings at this same level in the other pumping sessions. In addition, 16% of the samples obtained during unlimited simultaneous pumping had creamatocrit readings of 13% or higher, compared with 10% of readings at this level when other pumping regimens were used (Table 3). Table
3. Creamatocrit
readings by pumping regimen used
Pumping regimen
Range WI
SMinute 5-Minute Unlimited Unlimited
o-13 o-17 o-14 o-15
sequential simultaneous sequential simultaneous
Creamatocrit Median 6 6-7 6-7 7-8
readings Mean 6.52 7.26 7.18 7.70
Mothers’ preference of pumping regimen In addition to the quantitative measures reported above, the mothers were asked which pumping regimen they preferred and why. By a margin of three to one in this study, women preferred the double pump system over the single sequential option. In nearly all cases where the double-pump system was preferred, the amount of milk obtained and/or the woman’s perception that such pumping took less time, were mentioned. This preference held even when controlling for the participants’ milk volumes during the single and double pumping sessions. For example, during the timed pumping sequences, 67% of the women who’obtained more milk when pumping sequentially still preferred the simultaneous double
SEQUENTIAL
AND SIMULTANEOUS
BREAST
PUMPING
263
pump option. Of those women who obtained more milk when using the double pump option, 87% preferred that pattern over single sequential pumping. The same pattern was observed when the pumping sessions were allowed to proceed until each participant had ceased obtaining milk. Mothers who preferred the single-breast pumping option mentioned that they felt ‘cow-like’, that pumping both breasts simultaneously was awkward for them, or that they preferred to have one hand free for other activities even when they were aware that they obtained more milk using the simultaneous system. Among mothers who preferred to pump sequentially, mean milk volumes declined slightly when they used simultaneous pumping, whether they were timed or untimed (Table 4). By contrast, women who preferred simultaneous pumping experienced a marked increase (26%) in milk volumes obtained during timed pumpings, and a somewhat smaller increase (17%) in milk volumes during unlimited pumping regimens when they pumped both breasts simultaneously. Table 4. Pumping preferences by regimen and milk volumes obtained Pumping regimen
5-Minute J-Minute Unlimited Unlimited
sequential simultaneous sequential simultaneous
Milk volumes obtained Simultaneous Sequential Range Mean Mean Range (g) (9) (g) (9) 26-140 25-130 48-152 21-132
78 65 (-17%)’ 89 69 (-13%)
25-240 32-230 27-287 50-297
R
R?
F
Timed pumping sessions x pumping preference:
0.43
0.18
2.55
p-value < 0.05 >O.lO
Untimed pumping sessions x pumping preference:
0.50
0.25
3.69
